Field of the Invention
This invention relates to a hydrostatic axial piston machine utilizing a bent-axis construction having a driveshaft with a drive flange located inside a housing and rotatable around an axis of rotation. A cylinder barrel is located inside the housing and is rotatable around an axis of rotation. The cylinder barrel includes a plurality of piston bores. A longitudinally displaceable piston is located in each piston bore. The pistons are fastened to the drive flange in an articulated manner. The drive flange is supported on a housing-side slide face by an axial bearing that is in the form of a hydrostatically relieved sliding bearing having a plurality of slippers, each of which is mounted in an articulated manner on the drive flange, and each of which is provided on the end surface facing the slide face with a pressure pocket in communication with an associated displacement chamber of the axial piston machine for the supply with hydraulic fluid.
Description of Related Art
In hydrostatic axial piston machines utilizing a bent-axis construction, the longitudinally displaceable pistons located in the cylinder barrel are generally fastened to the drive flange of the driveshaft by a ball joint. The piston forces are transmitted by the piston to the drive flange located on the driveshaft and generate a torque.
Generic axial piston machines employing a bent-axis construction have significantly higher maximum allowable speeds of rotation than axial piston machines utilizing a swashplate construction, so that axial piston machines utilizing a bent-axis construction have advantages for use as a hydraulic motor.
In axial piston machines utilizing a bent-axis construction, the axial forces resulting from the piston forces can be supported by means of the drive flange and the driveshaft with a roller bearing. An axial piston machine of this type utilizing a bent-axis construction is illustrated, in FIG. 5 of DE 101 54 921 A1. The roller bearing of the driveshaft is formed by tapered roller bearings arranged in pairs. On account of the high axial forces to be absorbed, these two tapered roller bearings are correspondingly large to achieve a sufficiently long useful life. However, large bearings of this type occupy a great deal of space and, on account of the high inertial forces that occur, limit the maximum allowable speed of rotation of the axial piston machine.
To overcome these disadvantages, the axial forces in axial piston machines utilizing a bent-axis construction can be relieved by an axial bearing in the form of a hydrostatically relieved sliding bearing on a housing-side slide face. As a result of the hydrostatic relief of the axial forces, the roller bearing system of the driveshaft and of the drive flange can be made smaller and the limit speed of rotation of the axial piston machine can be increased on account of the lower inertial forces.
For the design of a hydrostatically relieved sliding bearing as an axial bearing, pressure pockets can be formed in one axial end surface of the drive flange with which the drive flange is in contact with a housing-side slide face, which pressure pockets are in communication with the displacement chambers for the supply of hydraulic fluid. To achieve a contact of the drive flange on the housing-side slide face that forms a sealing surface for the pressure pockets, the drive flange is in the form of a component that is separate from the driveshaft and is movable in the axial direction relative to the driveshaft. By means of a torque connection, such as a spline gearing, the drive flange is connected torque-tight with the driveshaft. Axial piston machines of this type are known, for example, from FIGS. 3 in DE 101 54 921 A1, U.S. Pat. No. 4,872,394 A1 and U.S. Pat. No. 3,827,337 A1. In axial piston machines of this type utilizing a bent-axis construction, there is no tipping of the drive flange away from the housing-side slide face at high speeds of rotation. Tipping of this type leads to an opening of the seal gap on the hydrostatically relieved sliding bearing and to a resulting increased loss of hydraulic fluid by leakage on the hydrostatic sliding bearing. One disadvantage of these axial piston machines, however, is that the torque connection necessary for the transmission of torque between the drive flange and the driveshaft entails a great deal of extra construction effort and expense and is complicated to manufacture. On account of the high stresses and loads that occur in the torque connection, which can be in the form of a spline shaft gearing, the maximum torque that can be transmitted at the torque connection, which equals the output torque of the axial piston machine, is limited. In addition, on account of the drive flange that is provided with pressure pockets, it is not possible to compensate for irregularities in the housing-side sealing surface that result from component deformations as a result of the pressure applied.
For the design of a hydrostatically relieved sliding bearing in the form of an axial bearing, it is possible in axial piston machines utilizing a bent-axis construction to locate longitudinally movable slippers in the drive flange that are in contact with the housing-side slide face and are provided with a pressure pocket which is in communication with an associated displacement chamber for the supply of hydraulic fluid. Axial piston machines utilizing a bent-axis construction of this type, in which the axial forces are hydrostatically relieved by means of slippers that are located between the drive flange and the housing, are known from FIGS. 1 and 4 in DE 101 54 921 A1, U.S. Pat. No. 3,198,130 A1, and U.S. Pat. No. 4,546,692 A1. With a hydrostatic sliding bearing of this type using slippers, the drive flange and the driveshaft can be constructed as a single piece so that there is no need for a strength-critical connection between the drive flange and the driveshaft. To ensure that the axial sealing faces of the sliding bearing (formed by the housing-side slide face and the end surface of the slipper) can be properly aligned and oriented with respect to each other to form an effective seal, it is necessary to mount the slipper in the drive flange in an articulated manner and so that it is longitudinally displaceable. An articulated bearing system for the slipper in the drive flange is necessary because a correct orientation of the drive flange with respect to the housing-side slide face is not possible on account of manufacturing tolerances and the deformations that occur during operation of the axial piston machine. Partial compensation for irregularities on the housing-side slide face that occur as a result of component deformations under the applied pressure can also be achieved by the articulated bearing system of the slippers in the drive flange and thus an installation of the slippers in the drive flange in which they are capable of executing a tipping movement. However, one disadvantage with axial piston machines of this type utilizing a bent-axis construction is that at high speeds of rotation, as a result of the strong centrifugal force acting radially outwardly, in connection with the articulated connection of the slippers in the drive flange, the slippers can tip away from the housing-side slide face. Increased leakage can occur at the hydrostatically relieved sliding bearing that reduces the efficiency of the axial piston machine. The maximum allowable speed of rotation is therefore limited on account of the leakage losses that occur as a result of the tipping slippers.